This invention relates to a device for advancing the main drum in a circular hose or the like knitting machine.
As is known, the main drum of such machines is provided with a plurality of lugs or juts arranged on its peripheral surface in conformity with the machine knitting program, and must be advanced stepwise or continuously over short distances, in order for it to actuate the various operational components of the machine as required. For the advance movement, a ratchet and pawl mechanism is utilized which comprises at least one pawl adapted for engaging a sawtooth ratchet wheel rigid with the drum itself, the pawl being moved back and forth in synchronism with the needle cylinder(s).
A device of this type is disclosed in Italian Pat. No. 909,716 granted to Francesco Lonati. Three pawls are provided in that device: namely, a primary pawl operationally associated with the programming chain of the machine to advance the drum by one step at predetermined times; and two secondary pawls which can be moved alternately back and forth to further advance the drum through more steps, if necessary. Both the primary pawl and secondary ones are disengageable from the teeth of the ratchet wheel, the former by raising upon control by the chain, and the latter by means of a raising movement set up by pins arranged at the wheel sides in accordance with a preset program. Thus, it becomes possible to not only advance the drum through one or more steps at a time, but also to do so continuously. The possibility of disengaging the pawls as desired affords a reduction in the number of drum advancing steps while knitting, and accordingly of the drum dimensions.
The movement of the pawls is continuous, even while raised, because it is derived through levers controlled by the profiles of respective disk cams which rotate in synchronism with the needle cylinder(s). The cams are configurated and rotated such that the primary pawl is reciprocated back and forth once every two revolutions of the needle cylinder, and each secondary pawl performs four such back and forth movements, distributed over two revolutions of the cylinder(s), the oscillations of the latter being mutually alternated.
That device has proved itself to be particularly advantageous, owing both to the rationalization of the drum movements and to its simple design and quick possibility of adjustment to suit a variety of knitting programs. By providing a primary pawl which is controlled directly by the machine main chain, the drum is ensured to always start in timed relationship with the cylinder(s), i.e. with the same reference generatrix of the cylinders.